Hub and spindle assembly having asymmetrical seals for a disc drive memory system

ABSTRACT

A rotating hub and fixed spindle assembly with first and second fluid dynamic journal bearings and first and second fluid dynamic thrust bearings for a disc drive memory system has a pump seal and a radial ring seal at a first axial terminus for lubricant containment, and a capillary seal and a labyrinth seal at a second axial terminus for lubricant containment and storage. Lubricant fluid pressure differences between first and second seals are minimized through one or more lubricant fluid communicating channels in the hub assembly, in order to minimize lubricant fluid loss through a seal. Lubricant fluid can also be purged of any air bubbles by lubricant fluid circulation through the channel.

TECHNICAL FIELD

The present invention relates to the field of hub and spindle assembliesfor disc drive memory systems, and in particular to hub and spindleassemblies having fluid dynamic bearings and associated lubricant seals.

BACKGROUND ART

Disc drive memory systems have been used in computers for many years forstorage of digital information. Information is recorded on concentricmemory tracks of a magnetic disc medium, the actual information beingstored in the form of magnetic transitions within the medium. The discsthemselves are mounted on a hub that is rotatably mounted on a fixedspindle. The information is accessed by means of read/write headsgenerally located on a pivoting arm that moves radially over the surfaceof the disc. The read/write heads or transducers must be accuratelyaligned with the storage tracks on the disc to ensure proper reading andwriting of information.

During operation, the discs are rotated at very high speeds within anenclosed housing by means of an electric motor generally located insidethe hub that supports the discs. One type of motor in common use isknown as an in-hub or in-spindle motor. Such in-spindle motors typicallyhave a spindle mounted by means of two ball or fluid dynamic bearingsystems to a motor shaft disposed in the center of the hub. Generally,such motors include a stator comprising a plurality of teeth arranged ina circle. Each of the teeth support a plurality of coils or windingsthat may be sequentially energized to polarize the stator. A pluralityof permanent magnets are disposed in alternating polarity adjacent thestators. As the coils disposed on the stators are sequentially energizedin alternating polarity, the magnetic attraction and repulsion of eachstator to the adjacent magnets cause the spindle to rotate, therebyrotating the disc and passing the information storage tracks beneath thehead.

The use of fluid dynamic bearing assemblies in such drive systems hasbecome preferred due to desirable reductions in drive size and noisegeneration as compared to conventional ball bearing drive systems. Influid dynamic bearings, a lubricating fluid functions as the bearingsurface between a spindle and a hub. Such bearings are of the journaland thrust types. Journal bearings fix the radial position of a hub asit rotates around a spindle. Thrust bearings constrain the axialposition of the hub as it rotates.

One, or the other, or both mating hub and spindle surfaces can bepatterned with grooves and lands in various patterns to make lubricantfluid pumps that are actuated by the rotation of the hub relative to thespindle. Such pumps can maintain lubricant fluid pressure gradientswhile the hub is rotating, providing thrust and journal bearingfunctions. When the hub is not rotating, lubricant fluids are maintainedin place in the hub to spindle gap by capillary forces.

For disc drives having first and second covers mounted to the spindlefor improved mechanical stability, lubricant fluid loss is inevitable atboth termini of the spindle, and is an operational lifetime limitingfactor for such disc drives. Sealing techniques include capillary sealsand labyrinth seals. Capillary seals are flared channels that rely onthe surface tension of the lubricant fluid to form a meniscus as thewalls of a channel flare apart. Capillary seals can also serve asreservoirs for lubricant fluid, but they are prone to lubricant lossthrough evaporation at the surface of the meniscus. Labyrinth seals canbe used with capillary seals to further reduce lubricant evaporation byproviding an elongate pathway for lubricant vapor to escape.Unfortunately, effective labyrinth seals tend to consume a fair amountof space, and are therefore difficult to use at both ends of a spindle.Different seal designs can be used at each end of a spindle, but isimportant for the lubricant fluid pressures at the first and secondseals to be at nearly the same pressure to reduce the loss of lubricantfluid from the seal with the lower pressure.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a hub and spindleassembly for a disc drive having at least one journal bearing, first andsecond thrust bearings, first and second fluid seals adjacent to thefirst and second thrust bearings, and a channel for a lubricant fluidthat connects the first and second fluid seals. Additionally, lubricantfluid circulation through the channel tends to purge any air bubblesfrom the lubricant fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents an exploded view of a hub and spindle assembly accordingto an embodiment of the invention.

FIG. 2 a illustrates a cross-sectional view of a hub and spindleassembly according to an embodiment of the invention.

FIG. 2 b illustrates details of a radial ring seal according to afurther embodiment of the invention.

FIG. 3 illustrates a cross-sectional view of a hub and spindle assemblyaccording to another embodiment of the invention.

FIG. 4 illustrates a cross-sectional view of a hub and spindle assemblyshowing lubricant fluid and a fluid communication channel according toan embodiment of the invention.

FIG. 5 illustrates a cross-sectional view of a hub and spindle assemblyshowing lubricant fluid and a fluid communication channel according toanother embodiment of the invention.

FIG. 6 illustrates several top cross-sectional views of hub and spindleassemblies with fluid communication channels according to variousembodiments of the invention

FIG. 7 illustrates an operation of an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

FIG. 1 shows an exploded, cut-away view of a hub and spindle assemblyaccording to an embodiment of the invention. Spindle 101 is affixed tobase plate 105 according to any one of a variety of techniques wellknown to one of ordinary skill in the art, such as screwing, bolting,press fitting, welding, etc. First thrust washer 102 and second thrustwasher 103 are affixed to spindle 103, along the axis as indicated,likewise according to any one of a variety of techniques well known toone of ordinary skill in the art, such as press fitting. Items 643 and104 are cut-away sections (for purposes of illustration) of the journalbearing and hub assembly that rotates about spindle 101 when assembled.In some embodiments of the invention, journal bearing sleeve 143 and hub104 are separate pieces that are coupled together using any of a numberof techniques widely known by one of ordinary skill in the art (e.g.,press fit). In other embodiments of the invention, the journal bearingsleeve is an integral part of hub 104.

FIG. 2 a illustrates a cross-section of an assembled hub and spindleassembly according to an embodiment of the invention in which thebearing sleeve is an integral part of hub 104. Like numerical referencesrefer to like drawing elements in all of the drawings. Spindle 101,first thrust washer 102, second thrust washer 103 and base plate 105 areall fixed together and stationary with respect to each other. As usedherein, a washer means a cylindrical or truncated conical piece defininga coaxial cylindrical cutout or truncated conical cutout. First thrustwasher 102 and second thrust washer 103 are washers disposed adjacent tothe first and second ends, respectively, of spindle 101. The thrustwashers may be separately fabricated pieces that are assembled withspindle 101, or in other embodiments one of the thrust washers may beformed as a protruding annular ring that is integral to spindle 101.

Hub 104 rotates relative to the spindle 101. Spindle 101 is patternedwith fluid dynamic pump patterns 109 to create a pair of journalbearings, regions in which the lubricant fluid pressure is elevated. Thepatterns comprise lands and grooves that compress the lubricant fluid tothe center of each band pattern 109. Although chevron patterns 109 areillustrated in FIG. 2, other pattern options are well know in the art offluid dynamic bearings.

The surface 108 of first thrust washer 102, that faces the second thrustwasher 103, is also patterned as a fluid dynamic pump to create anannular area of increased lubricant fluid pressure to form a firstthrust bearing. Likewise, the surface 110 of lower thrust washer 103,that faces the first thrust washer 102, is patterned as a fluid dynamicpump to create an annular area of increased lubricant fluid pressure toform a lower thrust bearing. An example of fluid pump pattern for athrust bearing is a sequence of chevrons wrapped in an annular patternaround the annular surface of the thrust washer.

Referring again to FIG. 2 a, lower thrust washer 103 conically taperstoward spindle 101 proximate to base 105 to create a flared annular gap114 forming a capillary seal for the lubricant fluid (not shown). Firstthrust washer 102 is circumferentially patterned with pumping seal 107.Pumping seal 107 is a fluid dynamic pump that directs lubricant fluidtoward thrust bearing 108 when the hub is rotating. Radial ring seal 106is shown in cross-section. Referring now to FIG. 2 b, the radial ringseal provides a capillary barrier 305 to lubricant fluid 307 through itsflaring channel width 305, followed by a constricting channel width 304connecting with labyrinth seal 303. Whereas fluid dynamic seal pump 102serves principally to contain the lubricant fluid while the hub 104 isin rotation, ring seal 106 serves to contain the lubricant fluid throughcapillary action, and limit the escape of lubricant fluid vapor when hub104 is not rotating. In some embodiments, the interior of cavity 106 iscoated with a barrier film coating (“BFC”) to provide a high energysurface that can repel lubricant fluid, as an additional lubricantcontainment measure.

FIG. 3 illustrates an alternate embodiment of the invention. In thiscase, the fluid dynamic pumps for the thrust bearings are patterned onthe matching surfaces of the hub, 111 and 112. In general the fluiddynamic pumps may be patterned on either one, or both mating surfaces ofa fluid dynamic bearing. The choice of which surface is usually dictatedby cost and convenience of fabrication. Likewise (although notillustrated), the fluid dynamic pumps for the journal bearings can bepatterned on the inside of journal bearing sleeve.

FIG. 4 is a cross-sectional view of a hub and spindle assembly accordingto an embodiment of the invention showing lubricant fluid 115 in place.Note that the capillary seal surrounding second thrust washer 103 canserve as a reservoir for lubricating fluid. Evaporation of lubricantfluid from the meniscus 507 can be minimized because the bottom of hub104, and the adjacent surface of base plate 105 form a labyrinth seal201. In the illustrated embodiment, the journal bearing sleeve is anintegral part of hub 104.

This asymmetrical seal design provides for a capillary seal, that canalso serve as a lubricant fluid reservoir, at the second end of thespindle where a labyrinth seal is also conveniently formed to suppresslubricant fluid evaporation. The first seal is a fluid dynamic pumpseal, backed up by a radial ring seal for physically compact lubricantfluid containment. However, as discussed above, it is important that thefirst and the second fluid seals operate at nearly the same lubricantfluid pressures, in order to avoid a lubricant pressure level differencethat can lead to lubricant loss through at least one of the seals.Lubricant fluid communication channel 117 is provided to equalizelubricant pressures at both seals. Without such pressure equalization,generally the lubricant fluid pressure in the vicinity of the pump sealof the first thrust washer 102 is greater than the lubricant fluidpressure in the vicinity of the capillary, second seal (about oneatmosphere for the second seal) formed by the second thrust washer and afacing portion of hub 104. This can result in lubricant fluid beingpumped out of the second seal when the hub 104 is rotating. Lubricantfluid communication channel 115 allows for lubricant fluid flow from thefirst seal area to the second seal area to equalize lubricant fluidpressures. Also, the pump seal of first thrust washer 102 can sometimesinject air bubbles into the lubricant fluid 115. If such bubblesaccumulate, they can lead to fluid dynamic bearing failure. Thecirculation of lubricant 115 from the first seal to the second seal viathe journal bearing, and then from the second seal back to the firstseal via lubricant fluid communication channel 117 tends to purge suchbubbles so that they do not accumulate.

FIG. 5 illustrates a cross-section of an alternate embodiment of a huband spindle assembly with a lubricant fluid communication channel, inwhich the hub 104 and the journal bearing sleeve 643 are separate partsthat have been assembled together, as described above. The otherfeatures, and the operation of this embodiment are the same as describedabove in connection with FIG. 4.

FIGS. 6 a-6 c show top cross-sectional views of hub and spindleassemblies according to various embodiments of the invention. FIG. 6 aillustrates an embodiment in which hub 104 has an integral journalbearing sleeve (corresponding to the embodiment described in connectionwith FIG. 4), and can rotate around spindle 101. Lubricant fluidcommunication channel 117, is formed in the journal bearing sleeveparallel to the spindle axis. FIGS. 6 b and 6 c correspond to theembodiment described in connection with FIG. 5, in which the journalbearing sleeve 643 is a separate part that is coupled to hub 104. In theembodiment of FIG. 6 b, the lubricant fluid communication channel 118 isformed by the journal bearing sleeve 643 and a groove in a facingsection of the hub 104. In the embodiment of FIG. 6 c, the lubricantfluid communication channel 118 is formed by hub 104 an a groove in thejournal bearing sleeve 643 that faces hub 114. In all of these cases,the lubricant fluid communication channel runs the length of the journalbearing area and terminates at the first and second shoulders (917 and919, respectively, in FIGS. 2 a and 7). Although single fluidcommunication channels are shown in FIGS. 6 a-6 c, multiple channels maybe used in some embodiments to increase lubricant fluid communication.

FIG. 7 is a cross-section diagram useful to demonstrate the integratedoperation of an embodiment of the invention for review. Fixed spindle101 is irrotatably mounted to base plate 105. First and second thrustwashers, 102 and 103, respectively, are irrotatable mounted to spindle101 approximately as shown. Hub 104 is rotatably positioned coaxiallywith spindle 101. The facing portions of spindle 101 between first andsecond thrust washers 102 and 103, respectively, and the facing surfacesof the hub (or the journal bearing sleeve in some embodiments) is thejournal bearing area. The journal bearing area provides radial positionstability to the hub as it rotates with respect to the spindle. Thesurfaces of first thrust washer 102 and second thrust washer 103 thatface together form first and second thrust bearing portions, 111 and 110respectively, with first and second shoulders (917 and 919, respectivelyin FIGS. 2 a and 8) of the journal sleeve proximate to first and secondthrust washers (102 and 103, respectively. The first thrust bearingportion 111 limits axial movement of the hub 104 toward the first end ofspindle 101, while allowing the hub 104 to rotate. The lower thrustbearing portion 110 limits axial displacement of the hub 104 toward thesecond end of spindle 101, while allowing hub 104 to rotate.

A lubricant fluid 115 fills the gaps between the mating hub and spindlesurfaces for the journal bearing area. The lubricating fluid 115 alsofills the gaps between the mating thrust washer and hub surfaces for thefirst and second thrust bearing portions.

Spindle 101 is patterned with land and groove features formed in firstand second circumferential bands 109A and 109B, respectively, to formfirst and second fluid dynamic journal bearing pumps. A rotationalmotion of hub 104 imparts a rotational motion to lubricant fluid 115.The patterns of the bearing pumps cause the moving lubricant fluid totravel toward the center of each circumferential band, therebyincreasing lubricant fluid pressure in these circumferential regions toprovide fluid dynamic journal bearing function.

Similarly, the parallel facing surfaces 111 and 110 of first and secondthrust washers, 102 and 103 respectively, are patterned with land andgroove features formed thereon so as to increase lubricant fluidpressure in an annular band for each to provide fluid dynamic thrustbearing function.

The lubricant fluid 115 is sealed at the first and second ends of thespindle using different methods.

The outermost seal at the first end of spindle 101 is formed by ringseal 106, formed circumferentially on the first thrust washer 102 and/orthe mating surface of the hub. The ring seal comprises a capillary sealportion 305, and a tapering portion 304, connecting with a labyrinthchannel 303. When the hub is not rotating, a lubricant fluid meniscusremains in capillary seal portion 302 as a result of surface tension(see also 307 in FIG. 2 b). Section 304 of ring seal 106 tapers to andconnects with channel 303 that forms a labyrinth seal to also suppressevaporation of the lubricant fluid.

A fluid dynamic pump seal 107 of a groove and land pattern is formedcircumferentially on the first thrust washer between the ring seal 106and the first thrust bearing portion 111. When hub 104 is in rotation,pump seal 107 forces lubricating fluid 115 toward the first thrustbearing, thereby preventing escape through channel 301 to the outside ofthe hub and spindle assembly.

The second thrust washer 103 tapers downward in diameter toward thesecond end of the spindle. This forms channel 114 of increasing widththat functions as a second capillary seal for lubricant fluid 115. Thecapillary seal formed in channel 114 has a larger meniscus area than thecapillary seal 305 associated with ring seal 106, and thereby canfunction as a reservoir for lubricant fluid 115. However, the largermeniscus area means that the second capillary seal is more prone tolubricant fluid loss through evaporation. The gap 201 between hub 104and base plate 105 forms a rather extensive labyrinth seal to suppresslubricant fluid evaporation.

Thus the hub and spindle assembly has seals at the first end of thespindle to provide for good lubricant fluid containment in a compactstructure, and has seals at the second end of the spindle to provide alubricant fluid reservoir. A resulting problem, however is that the pumpseal 107 tends to increase the lubricant fluid pressure beyond what theseals at the second end of the spindle can contain, resulting in loss oflubricant fluid through the second seal. A solution to this problem isto provide a lubricant fluid communication channel 117 between the first102 and second 103 fluid dynamic thrust bearings. A lubricant fluidcommunication channel can be implemented according to, for example, theembodiments discussed above in connection with FIG. 6. As long thetermini of the channel does not substantially interrupt so much of theannular fluid dynamic thrust pump band areas 110 and 111, first andsecond thrust bearing functions is maintained. The circulation of thelubricant fluid from the second seal to the first seal, and back again,tends to purge any air bubbles that may be injected into the lubricantfluid by the pump, first seal.

The present embodiments of the invention thereby use first and secondseal types that are appropriate for their position and function in thehub and spindle assembly, while using channels for pressurecommunication between the first and second seals in order to minimizelubricant fluid loss. The resulting benefits include a more compact huband spindle assembly size and a prolonged operational life.

Other features and advantages of this invention will be apparent to oneof ordinary skill in the art who studies this invention disclosure.Therefore the scope of this invention is to be limited only by thefollowing claims.

1. A hub and spindle assembly for rotating load coupled to the hubrelative to an axis, comprising: a spindle having a spindle axis, andfirst and second ends; a hub disposed coaxially to the spindle, that isrotatable relative to the spindle axis; a first thrust bearing adjacentto the first end of the spindle; a second thrust bearing adjacent to thesecond end of the spindle; a journal bearing disposed between the firstand second thrust bearings to limit the radial movement of the hub asthe hub rotates about the spindle axis; a first fluid seal that includesa fluid pump disposed to pump fluid toward the first thrust bearing,adjacent to the first thrust bearing; a second fluid seal adjacent tothe second thrust bearing; and a channel that communicates a lubricantfluid between the first and second fluid seals.
 2. The assembly of claim1, wherein the hub defines the channel connecting the first and secondfluid seals.
 3. The assembly of claim 1, further comprising a journalbearing sleeve coaxially positioned within, and coupled to the hub. 4.The assembly of claim 3, further comprising a groove formed in thesurface of the journal bearing sleeve, facing the hub, and forming thechannel connecting the first and second fluid seals.
 5. The assembly ofclaim 3, further comprising a groove formed in the surface of the hub,facing the journal bearing sleeve, and forming the channel connectingthe first and second fluid seals.
 6. The assembly of claim 1, whereinthe first thrust bearing includes a pattern of lands and grooves formedin a surface of the first thrust bearing.
 7. The assembly of claim 1,wherein the second thrust bearing includes a pattern of lands andgrooves formed in a surface of the second thrust bearing.
 8. Theassembly of claim 1, further comprising a first thrust washer adjacentto the first end of the spindle, wherein the first fluid seal includes acircumferential pattern of lands and grooves formed in the face of thefirst thrust washer facing the hub.
 9. The assembly of claim 8, furthercomprising a ring seal having a first circumferential groove with abarrier film coating formed in the first thrust washer, between thepattern of lands and grooves formed in the face of the first thrustwasher and the first end of the spindle, and having a secondcircumferential groove with a with a barrier film coating formed in aface of the hub facing the first circumferential groove.
 10. Theassembly of claim 1, further comprising a first thrust washer adjacentto the first end of the spindle, wherein the first fluid seal includes acircumferential pattern of lands and grooves formed in the surface ofthe hub facing the first thrust washer.
 11. The assembly of claim 1,further comprising a second thrust washer adjacent to the second end ofthe spindle, wherein the second fluid seal comprises an annular channelformed between the hub and the second thrust washer.
 12. The assembly ofclaim 12, wherein the annular channel widens toward the second end ofthe spindle.
 13. The assembly of claim 11 wherein the annular channel isat least partially filled with a lubricating fluid that terminates in ameniscus.
 14. The assembly of claim 1, further comprising first andsecond shoulder regions defined by the hub, the spindle, and first andsecond thrust washers, respectively, wherein the journal bearingincludes a pattern of lands and grooves on the surface of the spindlefacing the hub between the first and second shoulders.
 15. The assemblyof claim 1, further comprising first and second shoulder regions definedby the hub, the spindle, and first and second thrust washers,respectively, wherein the journal bearing includes a pattern of landsand grooves on the surface of the hub between the first and secondshoulders that faces the spindle.
 16. The assembly of claim 1, furthercomprising a base plate coupled to the second end of the spindle therebyforming a labyrinth seal as a gap between the base plate and a proximateparallel face of the hub.
 18. A hub and spindle assembly, containing alubricant fluid, for rotating at least one disk relative to a spindleaxis in a disc storage system, comprising: rotational bearing means forthe hub's rotation relative to the spindle; first and second axialfixation means for fixing the axial position of the hub on the spindle;first and second fluid seal means adjacent to the first and second axialfixation means, respectively; and fluid communication means tocommunicate lubricant fluid between the first and second fluid sealmeans.
 19. The hub and spindle assembly of claim 18, further comprisingmeans to purge bubbles from the lubricant fluid.
 20. The hub and spindleassembly of claim 20, further comprising means for storing a reserve oflubricant fluid.